1. Field of the Invention
The invention relates to an optical recording medium and in particular to a write-once optical recording medium having excellent high-speed recording characteristics and stability of data storage.
2. Description of the Prior Art
With the development of the Internet and increased capacity of computers, optical information recording media are desired to have a large recording capacity, recording a large amount data at high speed and can store information over a long time. Among various types of the optical recording media, the most widely used is write-once recording medium, such as compact disc recordable (CD-R) and digital versatile disc recordable (DVD-R).
Currently, the material used as the recording layer of write-once optical discs is organic dye including anthraaquinone cyanine indolizium and phthalocyanine (R. T. Young, D. Strand, J. Gonzalez-Hernadez, and S. R. Ovshinsky, Appl. Phys. Vol. 60, p. 4319, 1986; Y. Maeda, H. Andoh, I. Ikuta, and H. Minemura, J. Appl. Phys. Vol. 64, p. 1715, 1988; M. Takenaga, N. Yamada, M. K. Nishiuchi, N. Akira, T. Ohta, S. Nakamura, and T. Yamashita, J. Appl. Phys. Vol. 54, p. 5376, 1983). The information data are recorded utilizing changes in an optical characteristic caused by chemical change of the organic dye under irradiation of a laser beam.
The advantages of the organic dye are non-oxidation, low phase transmission temperature, high recording sensitivity and low cost. However, the disadvantages of the organic dye is as following:
1. It will cause large jitter values and distortion of disks due to poor conductivity.
2. It will cause poor durability due to low phase transmission temperature.
3. It will cause poor visible light absorption due to the short wavelength range absorption.
4. It will cause poor yield due to non-uniform coating for higher recording density PC substrate.
5. It will cause environment pollution due to organic solvent.
In order to improve the disadvantages of currently used organic dye with short range wavelength absorbed and non-uniform coating, it is desirable to replace organic dyes with inorganic materials as recording layer. The prior art (U.S. Pat. No. 5,252,370 and U.S. Pat. No. 5,334,433) disclose a write-once optical recording medium having a recording layer containing an inorganic compound, i.e. silver oxide or iron nitride. U.S. Pat. No. 4,477,819 and U.S. Pat. No. 5,458,941 disclose utilizing bi-layer inorganic material as recording media, and the materials therein are Ge/Al, Si/Al, GaSb/Ag.
Upon exposure to recording laser light, the microstructure of inorganic bi-layer occur changing, the recording mark were created via diffusion and mixing reaction within irradiating area. The space and recording mark cause a change of optical conditions. This enables digital data to be stored in media.